Because of its low cost and ease of use, Ethernet has become a favored technology for data transmission applications. In particular, telecom and wireless providers have begun to favor Ethernet in many of their core networks because of its associated benefits. However, many telecom systems are based on time division multiplexing (TDM), which works best in networks that can provide constant bit rate traffic for transmitting delay sensitive data such as voice and video, for example. The asynchronous nature of traditional Ethernet is not well suited for providing constant bit rate traffic. Without synchronization between communicating nodes (like in traditional Ethernet), variations in each nodes transmission frequency can cause overflow and underflow of data packets at a receiver.
One common way to achieve synchronization over Ethernet is Synchronous Ethernet (SyncE). SyncE architectures are described in ITU_T recommendations G.8261 and G.813. SyncE provides a mechanism to pass timing from node to node over the Ethernet physical layer. This mechanism gives telecom and wireless providers some assurance that networks based on SyncE can reliably perform in their delay sensitive networks.
SyncE implements the master/slave concept used in traditional Ethernet to pass timing from node to node. In traditional Ethernet, two communicating nodes operating under the master/slave concept are initially designated as master and slave, respectively. This designation occurs during the auto-negotiation process. During communication between the two nodes, the master generates a transmit clock locally from a free-running crystal oscillator and the slave recovers the master clock from data received from the master. The slave uses the recovered clock to transmit its own data.
For SyncE, the same master/slave concept is used to pass timing from node to node. However, the master/slave concept only allows timing to be passed in one direction between two communicating nodes; that is, from master to slave. The direction in which timing is passed cannot be dynamically switched between two communicating nodes without re-performing the auto-negotiation process. In order to guarantee a high reliability in SyncE networks transporting delay sensitive data, bi-directional delivery of timing between two communicating nodes should be possible without having to re-perform the auto-negotiation process, which can add significant delay and may result in an unacceptable link drop.
Therefore, what is needed is a system and method for allowing an Ethernet node to dynamically switch between master and slave designations without requiring the auto-negotiation process to be re-performed.
The present invention will be described with reference to the accompanying drawings. The drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.